Selecting resolution/ranges on a DAQ device for analog data acquisition

[davey31415]

Hi,

I believe when configuring a daq device for analog data acquisition the minimum/maximum voltage range select the resolution of the device much like selections on a multimeter do- is this correct?

I've noticed when selecting 0V to 2V the resolution is higher than -10V to 10V on the USB-6009.

I expect that the ranges are listed in the manual (I've requested a copy of the manual be emailed to me since my company's internet will not allow me to download it).

Is it possible to use a high resolution like I see on the 0V to 2V setting with higher ranges like 8V to 10V ?  Or for high resolution does the setting need to be centered or started at 0V?

[Christian Mergl]

With the min/max values you indirectly set the amplification for the ADC.

This causes the e.g. 16 bit to be spread over +/-1V or +/-10V or other possible ranges.

For sure the smaller the range the more accurate is your measurement.

If you want more accurate measurements for your +/-10V range you will need another hardware.

Christian

[hohk]

.

Just a question.

I am thinking of using the NI-6008 to measure mV range voltage readings from a piezoceramic sensor. So, if i select the DAQ range to be +/- 1V, i should expect the output readings to be small. Or could i just scale the output graph in SingalExpress to show it in the +/- 200mV range?  

As for the NI-6008 DAQ, is it suitable for measuring voltage readings for piezoceramic sensors at all? Or do i really have to use an expensive charge amplifier (or a DAQ with very high input impedance)? I need to take 4 sensor readings about 2kHz sampling rate per sensor. 

Any comments? 

[Dennis_Knutson]

You can use a DAQmx Device property node to read the possible ranges of your device. Also remember that setting the min/max causes DAQmx to choose the best possible range for your expected signal - it does not mean that your limits are the actual range. In your example, the device may use a -5/+5 range if that is the closest actual range supported.

[hohk]

Which means that if my sensor readings are 50mV and the smallest range the NI-6008 supports is +/- 1V, then will the output be too small for me to see or does the software automatically scales the graph to say..+/- 100mv. Which means that the range i set for the DAQ only affacts the accuracy (in this case it is 1.57mV) right? I cant really try it out myself yet because the DAQ is not in my hands yet..

[Dennis_Knutson]

What it means is that if you specify a min and max of +/- 50mv, the 6008 will use a range of +/- 1V since that is the closest supported range of the hardware when using a differential configuration. Select single-ended and the only range the hardware supports is +/-10V.

I don't know how you calculated 1.57mv. In diff mode, you have 12 bits and dividing 4096 (2**12) by 2 (+/-1V) is equal to .49mv. Pay attention to the system noise specs though.

Don't see where the scale of a graph has anything to do with the resolution of the hardware and how small of a signal you can acquire.

I would not have chosen this inexpensive device if I was required to read 50mv sensors.